1. Field of the Invention
The present invention relates generally to battery powered communication devices, and more particularly to a battery powered communication device which provides out-of-range battery saving.
2. Description of the Related Art
Communication devices which are operated from a battery have generally had limited operational lifetime, due largely to high receiver operating currents. Battery saving techniques have been developed, and have been widely used which significantly extend the operating lifetime of the communication device.
One of the most widely known battery saving techniques used by paging receivers can be found in the POCSAG (Post Office Code Standardization Advisory Group) paging format, in which the paging receiver has two modes of operation. The first mode is a modulation detection, or asynchronous, battery saving mode facilitated by the provision of a preamble of bit reversals. Good battery economy is provided in low transmission periods using short signal sampling periods.
The second mode is a time division, or synchronous, battery saving mode facilitated by the use of eight frames per batch. Good battery economy is provided by switching off the receiver during those frames in which the pager has no interest.
Other techniques for battery saving have been developed which utilize information located typically in the synchronization code word to extend the interval of time between the signal sampling periods, or through the use of an additional code word which defines a time interval during which the paging receiver will battery save. Because battery savings decisions are influenced by the relative signal strength at the receiver, signal quality measurements have also been used to improve the battery save decision making process, and have reverted to conventional asynchronous battery saving techniques when the signal quality is weak.
Communication devices, such as paging receivers described above, have used various techniques to improve battery life during periods of time when there is normal message traffic on the channel, when there is low message traffic on the channel, and when signal conditions on the channel are weak. Such communication devices have also reverted to conventional battery saving techniques when the communication device is out-of-range of a transmitter.
The use of conventional battery saving techniques can greatly impact battery life when a communication device is out-of-range of a transmitter. What is needed is a battery saving technique which can improve battery life when a communication device is out-of-range of a transmitter. What is also needed is a method by which a user of the communication device is notified that the communication device is out-of-range of a transmitter, and that the communication device is battery saving.